1. Field of the Invention
The present invention relates to a photovoltaic device that can be protected from electrostatic voltage even when touched by a charged worker.
2. Related Background Art
In recent years, increase in awareness of environmental problems has been spreading on a worldwide scale. Among others, concern is deep over the global warming phenomenon due to emission of CO.sub.2, and desires for clean energy source have becoming stronger and stronger. At present, solar cells can be considered to be one of hopes as a clean energy source because of their safety and easiness to handle.
There are a variety of solar cells, for example, typified by crystal silicon solar cells, polycrystal silicon solar cells, amorphous silicon solar cells, copper indium selenide solar cells, compound semiconductor solar cells, and so on. Among them, the thin-film crystal silicon solar cells, compound semiconductor solar cells, and amorphous silicon solar cells are recently under active research and development in various fields, because they can be formed in a large area at relatively low cost.
The cost of the solar cells now available is, however, still high, and it is thus necessary to further decrease the cost thereof. For that purpose, problems to be solved are, for example, as follows.
(i) Efficient utilization of electric power-generating region
(ii) Reductions in costs for connecting members at connecting portions and labor costs for connection
In order to improve above (i), it is necessary to increase the percentage of the electric power-generating region with regard to the area where the solar cell is installed. In order to improve above (ii), it is necessary to increase the area of solar cell.
FIGS. 8A and 8B are schematic views to show a conventional photovoltaic device improved in above (i) and (ii).
In FIGS. 8A and 8B, reference numeral 800 designates a photovoltaic device, 801 a flexible substrate, 802 a semiconductor layer, 803 a transparent electrode layer, 804 a positive electrode busbar, 805 collector electrodes, 806 negative electrode busbars, 807 an insulating tape and 808 solder. One end of the positive electrode busbar 804 of one photovoltaic device is soldered to a portion of the negative electrode busbar 806 of another adjacent photovoltaic device, thereby connecting these two photovoltaic devices. This connection is repeated with a plurality of photovoltaic devices to obtain a solar cell module.
The photovoltaic devices described above, however, has a low electrostatic withstand voltage and therefore causes the following problems. Here, the electrostatic withstand voltage in the present invention means a value of applied voltage that causes 10% decrease of Voc under 200 Lux between before and after application thereof when an arbitrary voltage is applied to the electric power-generating region of light-receiving surface.
(1) The electrode busbars-leading structure as shown in FIGS. 8A and 8B can decrease the non-electric power-generating region on the light-receiving surface side as compared with a case of leading both of the positive and negative electrode busbars on the light-receiving surface side. However, in order to minimize the effect of a flux used in soldering on the light-receiving surface of photovoltaic device in a series connection step, the series connection needs to be conducted while keeping the light-receiving surface side of photovoltaic device facing down. On that occasion, a tool used for the series connection might rub the light-receiving surface of photovoltaic device to generate the static electricity. When the charged tool or worker touches the photovoltaic device, the electricity will be discharged to the photovoltaic device in some cases. This sometimes resulted in damaging the semiconductor layer of photovoltaic device.
(2) For sealing the photovoltaic device with a resin, filler films or glass fibers are stacked on the light-receiving surface side, and thereafter the filler film is shifted for adjustment of alignment or the stacking is done over again, whereupon the static electricity will be generated. This sometimes resulted in damaging the semiconductor layer of photovoltaic device and thus failing to achieve sufficient electrical characteristics. It is the present status that countermeasures against the static electricity rely on facilities such as a wrist band, a table mat, a floor mat, or installation of the earth for prevention of charging, but they are far from sufficient.
(3) The photovoltaic devices are sometimes packed and conveyed before the sealing thereof with the resin. On that occasion, a spacer of slipsheet or foam is interposed between photovoltaic devices. When the photovoltaic devices are moved or taken out, friction generates the static electricity. The use of spacer of slipsheet or foam for prevention of charging was the cause of increase of cost as a result of the fact that reuse thereof was difficult.